Asphalts and mineral aggregates constitute the principal materials of construction for asphalt pavements. Asphalts (complex mixtures of nonpolar bituminous hydrocarbons derived from petroleum refining) exhibit a low affinity for water. In contrast, the surfaces of mineral aggregates are typically polar and highly-charged, thereby imparting a high affinity for water. These pronounced differences in polarity and water affinities result in the mineral surfaces of aggregates and asphalts displaying very low affinities for one another. Accordingly, asphalts often adhere poorly or not at all to the surfaces of mineral aggregates.
A consequence of poor adhesion is a short service life for asphalt pavement. The debonding of poorly adhered asphalt from aggregate is accelerated by the presence of water, which preferentially wets the aggregate (thereby causing the asphalt to strip-off the aggregate surface). The result of asphalt stripping from the aggregate surface is a flaked pavement and the formation of potholes.
Surface active amines are frequently added to asphalt formulations to reduce the water-induced debonding of asphalt from the surface of mineral aggregate. These surface active amines have polar head-groups that exhibit an affinity for polar surfaces like that of the aggregate. The surface active amines also typically contain long, non-polar fatty chains that exhibit a high affinity for asphalt. The molecular structure of the surface active amine serves to lower the interfacial tension between asphalt and aggregate, thereby increasing the strength of the adhesive bond between the two. As these surface active amines function to prevent the asphalt from stripping from the surface of the mineral aggregate, they are commonly known in the industry as anti-stripping agents.
Asphalt formulators have found that reacting these surface active amines with acids to form salt derivatives yielded increased adhesion between the asphalt and aggregate. For example, the use of carboxylic acids to neutralize certain fatty amine derivatives for use as anti-stripping agents is taught in U.S. Pat. No. 2,426,220 to Johnson. Falkenberg et al. teach the use of amidoamine salts of carboxylic acids in U.S. Pat. No. 3,230,104. The use of certain reaction products of amines and imidazolines with mineral acids as anti-stripping agents are taught in U.S. Pat. No. 3,868,263 to McConnaughay.
In addition to being utilized as anti-stripping agents, various amine salt derivatives are also commonly employed in mineral processing, ore flotation, and for metal corrosion inhibition.
However, a major problem exists with the utilization of these amine salt derivatives, particularly in plant environments. As fluidity at low temperatures is necessary for easy handling and pumping, it is required that these derivatives be liquids at temperatures below about 60.degree. C. Unfortunately, the mineral acid salts of fatty amines, fatty amidoamines, and other similar amine derivatives of fatty acids tend to be extremely viscous, often non-flowing, paste-like materials. Moreover, water or low-boiling solvents cannot be employed to fluidize these salts for use as anti-stripping agents in hot asphalt formulations, as the volatilization of the water or solvent causes the asphalt to both foam and cool (thereby producing handling and application problems).
The physical properties of these materials result from a number of factors. First, the materials have elevated melting points and highly-ordered salt structures. The formation of an ionic bond is conducive to crystallization and a concomitant rise in melting point and viscosity; while the micellular organization of components of like polarity result in the formation of ordered molecular structures. Furthermore, non-polar fatty chains preferentially associate with other fatty chains due to van der Waals attractions. Finally, the dielectric effects and ionic interactions compel polar ammonium salt moieties to associate with one another.
The problems associated with handling these paste-like materials has traditionally been addressed in one of two ways. One method has been to heat the mineral acid salts of amine derivatives until they are sufficiently liquified to handle effectively. However, this heating causes dissociation and the liberation of both free mineral acid and free starting amine--thereby reducing the chemical effectiveness of the salt composition. The other method commonly employed to address this handling problem in production plants has been to equip the plant with costly specialized equipment for pumping viscous pastes.
Therefore, an object of this invention is to solve these problems by disclosing water-free fluid mineral acid salts of fatty acid amine derivatives.
A further object of this invention is to disclose water-free fluid mineral acid salt compositions of fatty acid amine derivatives which are suitable for use as anti-stripping agents in hot asphalt formulations.